Calibrator for thermostats



Nov. 10, 1953 v. J. EVANS CALIBRATOR FOR THERMOSTATS 2 Sheets-Sheet l Filed Jan. 5, 1951 Vllnfl.

NOV. 10, 1953 \/n J. EVANS CALIBRATOR FOR THERMOSTATS 2 Sheets-Sheet 2 Filed Jan. 5, 1951 www Winlnllavvbon L INVENTOR.

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Patented Nov. 10, 17953 i' UNITED i PAT-ENT GFFICE CALIERTRFOR THERMSTATS Vincent J1 Evans, Lakewood, Ohio Application January 5, 1951,`s'eria1No.'204;621

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l In various `types of Aheating equipment; acom; mon-'practice is to control the heat'supp'liedby setta-ble "thermally r'esigionsivel controldevice. Though such control Vdevices' arel carefully calibrated andadjiisted at the factory nevertheless in the 'eldthey frequently fail 'to `respond accurately to the temperature setting selected'by the user and' must-be recalibrated 'either in a'repair'shop vor at the'site' :of use. I

*"Typic'al' exampleslof the uses in which there is' needfor 'recalibraticn 'and in which difficulties are lencountered in thel prior methods of vrecalibration aredome'stic gas lcooking ranges with thermostatically controlled oven 'burners andthe domestic"electricjcooking ranges vwith thermostatica'l'ly `controlled oven baking and broilin'g heating' elements.

For purposesA yof illustration'"hereinafter the present inventionis described as applied'todomestic cooking ranges', its use inconn'ection'with other equipment 'and theprob'leins 'arising' inconnection withthelatter being app`arent"froni the illustrative example.

Domestic gas." cooking *1"ar'1g'es, for example, usually are provided with an oven burner which is vcontrolled-by a thermally V-resi'aonsive *device comprising af iiuidpressure voperated gas valvel ref sponsiveto the' fluid pressure developed by aib'ulb type thermostat. Domestic electric cooliing range' ovensV usually are providedwithelectric heating elements Which are controlled "by ther'- mally responsive devices-comprising a huid-pressure operated'lelectric switchresponsive tothe same-bulb type thermostat.

ziIn both of these types of I'controldevices, the thermostat comprises an elongated -bu-lb'ofsniall diameter which contains a highly eXpansi-ble huid and which isf'conhectedby al suitable'fconduit to abellows or thev like n a-sealed 'system,thebe1 lows in turn being connected: to the lg'as""valve orfelectric switch tor operating the-saine. YThe device is` provided vvitha control knob byiwhich itc'an be set to open-and close the valve or switch inresponse to thechangelof iiuid pressurelreated by the-bulb or 'switchlso as'torn-aihtaintheteinperature indicated on a dial carried byftheknb. The control device Agenerally is concealed-behind the top frontwpanelof the range 'with a stemffex'- tending throughfthe'front Lpanel` and the knliis mounted adjustalolyv thereon anch-is accessible from) the front of` the range. The bulb :isfarranged in the ovenl to 'becfo'ntrolled 1 Considerable difficulty has .,-arisen iin. "the calibrating of such ther-m'allyvresponsivefcontroleevices, 'particularly in the homev or workshop. iIn

accordance with the prior methods; thedeviceis adjusted by turning on ithe 4:heatY in 'the oven, setting" Vthe` dial"V to ar preselected temperature, usually about-3CD Fahrenheit; and vthen allowing 'the'oven toheat u'rrdert'he control of the thermostat'ior' ajp'eriod 'of from forty-ve minutes to one hour," depending uponfthe rate of heating 'of the particular "burner" `and v'otherV ieharact'eristics of the range. The purpose of this is to assure thatl the oven hasreached 'av constant temperature. A suitable tlie'rm'omet'eris placed intheoven to determine the actual temperature and, at the instant of "opening the oven, is read and 'theny comp-a'red"with *the 'dial"setting If the dial' setting does not agree withl thethermometer, the knob set screw is loosened' and the knob rotated 'relative to' the" stem until the dial` reading agrees-with the therr'nonieter; 'and then Asecured in rotated position, fter"suclr ``setting thel 'thermostat' is usually checked again, again allowing a'c'oiisiderable 'period"of itime'to assure that `'the"'ovenl 'has reached a rconstant temperature.

Attempts to shorten vthe time for testing usually results' in iinpr'oper adjustment and subsequent heine service' calls for' 're-adjustment.

' -It is aii v'object 'ofthe' 'present invention' to' make possiblethe 1`t:"aliloration vof such 'thermally 'responsive'controldevices inthe oven-Within a `'period of five to tenl ininute's 'and Without the" necessity ofv heating 'the' oven.

in" accordance 'withl the vpresent invention a calibrator'i's provid'edwhich comprises essentially a hollow casing of 'verylimited-volume in which is an electric heating element operated by'the usual himselioldl supply/of 1l() to 115 'volts'` of alternatingicuirent and'controlled by a normally "closed thenlostatically operated swtch'wliich is adapted to'ope'n *at a predetermined temperature. Afmeans is"prov'-idedi in ft-he casing for 'receiving the' bulbl ofthe thermally responsive device' to` be tested'so i 'that lfthe-"bulbis responsive to: an faccuratelypredeternihed temperature provided `by the controllediheat'ig element. VAll'rialrtsir the casing' are in'clo proximity to each' other andv as agp are' s'xidd by heal'. insulating- 'Inail-erial so as to provide a constant temperatureliat the received! bulb 1^' in afi` matter ofi Lve i' to- Aten minutes. scmellinstances two thermostatically operated switches Varelprovi'dedfin thecalibr-'at'or solthatTthe "arnpliti-ide,A that is, bothlthe l'ovvfturnon= temperatrefand nigh #cut-off temperature, ofl the dvicefbeing @tested can be" determined.

sive control devices one at a time, while they are installed in the ovens of domestic ranges, it being apparent that bench type modifications of the present calibrator can be provided so as to calibrate a large number of such devices concurrently in a workshop when they are disassociated from the ranges.

More specic objects and advantages will become apparent from the following description, wherein reference is made to the drawings, in which;

Fig. l is a top plan view of a calibrator embodying the principles of the present invention, part thereof being shown in section for clearness in illustration;

Fig. 2 is a longitudinal vertical sectional view of the calibrator illustrated in Fig. l and is taken on line 2 2 of Fig. l, part thereof being shown in elevation;

Fig. 3 is a cross sectional view taken on the line 3 3 of Fig. 2;

Fig. 4 is a wiring diagram showing the electric circuit used in the calibrator of Figs. l through 3;

Fig. 5 is a fragmentary diagrammatic side elevation of a portion of an oven of a gas range showing the thermally responsive control device for the burner and the manner in which the present invention is used for Calibrating the same;

Fig. 6 is a longitudinal sectional View, similar to Fig. 2, showing a modified form of the invention;

Fig. 7 is a wiring diagram showing the electric circuit employed in the modined form of the invention; and

Fig. 8 is a diagrammatic illustration and wiring diagram showing the application of the modincd form of the invention to an electric oven for both Calibrating the control device and checking its amplitude.

Referring first to Figs. l through 3, the device comprises essentially an elongated casing I of small cross section, which is closed at the ends by suitable caps 2. Mounted within the casing I is a supporting means for the bulb of the thermostat to be tested. In the form illustrated, this support comprises a metal tube 3 which prefer'- ably extends the full length of the casing and is securely anchored at its ends in the caps 2, for example, by suitable nuts so that the tube acts both as a support for the bulb and as a reinforcing means for the casing itself. The tube 3 eX- tends slightly beyond the ends of the casing I and is open at both ends.

Mounted in the casing I, beneath the tube, is an electrical resistance heating element 5 which is preferably supported from the tube by means of suitable brackets 6 in slightly spaced relation to the tube. The element 5 preferably is coextensive in length with the tube 3 and almost as wide as the casing I. The heating element may be of the enclosed resistance wire type, the resistance wire 'I being wrapped on a suitable mica core 8 and covered on the outside, in turn, by suitable mica or other heat conducting insulating material 9.

Also mounted within the casing I in close proximity to the heating element 5 is a thermostatic electric switch, indicated generally at I0, having a movable make and break contact II operated by a suitable low expansion metal bridge I2 and a stationary contact I3. The contact i3 may be adjusted by a suitable screw I4 for varying the position of the contact I3 so as to determine the amount of movement required for the make and break contact I I to make and break contact, thus predetermining the temperature at which the switch opens and closes.

Within the casing is a pilot light I5 which is visible through a suitable opening or port I6 in the end. wall of the casing.

As best illustrated in Fig. 4, the resistance element 5 and pilot light I5 are connected in parallel with each other so that the pilot light indcates the operativeness and inoperativeness of the heating element and cycles on and ofi therewith. Connected in series with the parallel connected heating element 5 and pilot I5 is a thermostatic switch El). The main power leads of the circuit, indicated at il, are provided with the usual saber connections, as indicated at I8, for plugging into the usual vwall receptacle so as to connect the calibrator to the usual 110 to 115 volt A. C. power source. All of the elements within the casing I are wrapped in suitable heat insulation material I9, such as asbestos or glass fibre, so as to corinne all of the heat substantially to the tube or bulb support 3. Thus the thermostatic switch Iii can be set at a predetermined temperature and within ten minutes from cold the tube 3 has reached a constant predetermined temperature.

Referring next to Fig. 5, there is shown an oven 26 of a domestic gas range which is to be heated by a burner Ei. Any conventional settable thermally responsive control device 22 is provided for controlling the burner and is regulated by a suitable knob 23 having at its base the usual dial with temperature indicia thereon. The device 22 is operated in response to changes in iluid pressure developed in a thermostatic bulb 24 to which it is connected by means of a suitable easily bendable tube 25, usually of copper.

In order to calibrate the control device, the calibrator of the present invention is placed in the oven on the usual open tray or grid with its pilot light I5 positioned at the bottom and is plugged into the usual household circuit. rlhe bulb 24 is inserted into the tube 3. Within about ten minutes, from cold, the temperature within the tube 3, and that of the bulb, has reached a constant value which has been pre-selected by setting of the thermostat Iii. Usually this teniperature is 300 Fahrenheit. The bottom pan of the oven is preferably removed so that the oven burner flame can be observed. After the calibrator has remained on for about ten minutes, as described, the oven burner is turned on by the knob 23 and lighted, the door of the oven remaining open. The knob 23 is then turned so as to reduce the flame until it is burning on the by-pass circuit which supplies gas only for a temperature below that controlled by the control device. Next, the dial is rotated toward higher temperature slowly until the oven flame increases slightly. This increase indicates that the device 22 has just come under the control of the thermostatic bulb 2li which is calling for more heat. Since the temperature of the bulb 2li as applied by the calibrator is known, the dial of the knob 23 is read and the difference between the dial indication and the true temperature to which the bulb is subjected is determined and the dial set to correspond to the true bulb temperature. Usually the dial is reset by loosening the knob set screw, turning the knob relative to the stem of the device so that the dial indication is that for which the calibrator is set, and then securing the knob against rotation relative to the stem.

The calibrator is then disconnected from the aoissgeso electric circiut and-ithe'bulb restored 'toits originalpositioninthe'oven.

Inan-fe1ectricovenfit'is desirable toch'eck not only the` `ealibr'ationof the A'thermostatic bulb of the control'deviceffora 'given temperature but alsoito 'check' its amplitude. `lor"thispurposethe form/of the'deviceillustratedin'fFig. 6 Withthe wiringl diagram `f' illustrated 'in Fig.V '1- is employed.

The latter structure.v fin general; the ysame as that- -heretofore described Y except that, 4inV addition-to a thermostat, "such as' the thermostat 'l0 heretofore describedyand such as indicated at 25,^in'-`Fig. 6, vthe'device-is provided with a second thermostat 21. *As in the-prior device the `heatingvelement, indicated 'at 28, visV -connected'in parallel' with the pilot xlight 33 and the parallel connected element' -28L and "light 30 are connected in series with the fthermostati 26l which-operates inthe v'samemanner-as the thermostat i3 and which 'is the low temperature thermostat, usually set to-openand breakthe circuit ataboutB'S()o Fahrenheit. The additional 'thermostat 21 is "the same 4type of thermostat as the thermostat V23' but isset'to open at a temperature'of about 370 Fahrenheit. The thermostat 21 is'connected 'in a bye-pass circuit around the thermostat 25, and a manually' controlled switch 3|` is 'provided in v this by-*pass circuitin'serieswith the thermostat 21. v`Both'thermostats are normally closed. With the 'switch 3 l open,- this 'modification orv the clem viceisplugged 'into the'usual l1() volt'household circuit whereupon it operates in the same manner as the one heretofore described.

To^better understand the use of 'the present invention' 'in the "calibration 'and 'checking of amplitude of a thermally responsive control deviceof 'a'domestic electric' cooking'range oven there'is illustrateddiagrammatically in Fig. 8' a Wiring diagram and the control device of one type ofv electric range' oven.

'Referring' to Fig. 8, the oven' is'provided'with a baking heating element 32 and a' broiling'heating element 33 both of whichare' controlled by means of a 'thermally responsive control device 34-which preferably iswof -theexpansiblemfluid type employing an elongated bulb 35 similar to the bulb 24-heretofore described.

The 'control device 34 is provided with the usual rotatablecontrol knob 36having indiciafthereon designating the temperature and being operable upon rotation. to set the control' means at `the temperaturei desired. For Ythis ypurpose, as is usual in such devices, the knobismounted onran operating stem 31 which is arranged to extend through the front panel of the range. The knob is secured for rotation with the stem 31 by means of a set screw which can be loosened for adjusting the relatively rotated positions of the knob and stem. The control means 34 includes a main thermostatically operated switch 38 for opening and closing the power circuit to the heating elements 32 and 33 in response to the operation of the fluid pressure developed in the bulb 35.

Since the two heating elements 32 and 33 are usually used selectively they are provided also with individual mechanically operated switches. For example, the baking element 32 is Provided with a normally closed switch 39 and the broiling element 33 is provided with a normally open switch 40, these switches being arranged between the main thermostatically operated switch 38 and the elements, respectively. The switches 39 and 40 are operated by means of a pin 4| under the control of a cam 42 which is mounted on the the baking element 32 is' connected-bythe switch "39 tothe `switch '38 and by; thelatterf when closed, to the source of power. This connection continues for all'rotated positions of the knob'36 from off toward on position' until afpre'selectled higher -temperature setting, usually above 'lthe range of the element32,=-is reached-'whereupon the normally closed switch '39 is opened'by' the cam and-"concurrently the :normally open switch is closed.' after4 which the 'broiling elementx 33 only is"`under the' lcontrol'of Xthe 'switch5-38. VThus both- 'elements are l'selectively'brought under the control'of thercontrolidevice -34 and th'ere'foreof the" bulb 35.

4A pilotI light 43 is' 'connected inparalleli with the baking element 32 to-'indicate when it is-oif and"on.

'"In"order "toL calibrate thel Icontrol device `34, either'calibrator'described is' placed inthe'pven as heretofore described'and `the'bulb inserted and the"'calibrator 'thermostatI isr set- -forafbreselected temperature; orexamplep Fahrenheit. After about ten minutes the dial 3Ejstarting at off position *isturnedY slowly 'until Ethe pilot 'light43comes on. The ldial 35 lis then turned slowly'in the'opposite direction until lthe pilot llightv 43 'snaps oir". This "is repeated-several timesjthe' readings being"-noted. Half--way=be tween thesev v'readingsl is `rthe preselectedvtemperature 'of' 300 Fahrenheit. *Accordingly-the dial set screw is loosened and the dial 35 is rotated to 300 Fahrenheit, or the preselected temperature, and secured in place.

In order to test the amplitudeofl the control device of Fig; 8, the'calibrator'of Figs. 6 and 'lis used. The' knob '36 ofthe control device'may be turned to about half way between 'the high 'and low temperatures" at which the' 'thermostats 26 and 21'are set; respectively. The calibrator' is plugged'in, the bulb '35 inserted, Yand'allowed `to reach constant low' temperature. I'lor'exampla using 330'Fahrenh'eit for Vthe low'limit thermostat 26 and`3'70o Fahrenheitfor the high limit thermostat'21, the 'knob '3B maybe' 'set for"350 Fahrenheit. 'With the switch 3l closed, the temperature of the calibrator and'bulb 35 is'"raised from 330'Fahrenheit toY 370 Fahrenheit "'Sin'ce theknob is set for 350"Fahr'enheit, 'the bulb 35 should open lthe switch' 38 within'a sh'ort while after closing of the switch 3|'and beforethe time 'the thermostat" 21 cuts off at 370"V Fahrenheit. The opening of the switch 38 is indicatedI by the pilot light 43 going oi. After the bulb 35 opens the switch 38, the switch 3| is opened, whereupon the temperature of the calibrator drops within a short while to 330 Fahrenheit. Before the thermostat 26 closes, however, the bulb 35 should close the switch 38. Such is indicated by the pilot light 43 coming on. Thus the amplitude of response of the control device is readily determined without the time consuming job of repeatedly heating and cooling the oven.

Obviously, the calibrator itself must be maintained operative within accurate limits and is usually set accurately at the time of manufacture. It may be tested either by means of insertion of a thermometer in the tube 3 or by testing it with a thermostatic electric switch known to be accurate, the latter being preferred because it does not have to be connected to any device as the click of its snap mechanism may be heard easily and indicates the temperature reached by it.

As mentioned, the present calibrator is shown for testing one or two thermally responsive devices at a time. Obviously it can be made with a plurality of bulb receiving tubes with a common heating element, or individual heating elements, for use in a workshop where a larger number of control devices, disassociated from the ranges, are to be tested concurrently.

Having thus described my invention, I claim:

1. A calibrator for a thermally responsive control device and comprising a hollow casing, supporting means in, and extending endwise of, the casing and adapted to receive a thermally responsive element of the control device, said casing having an end wall with an opening therein for permittinginsertion of the thermally responsive element into the casing in proper psition on the supporting means, an electric heating element in the casing and extending endwise thereof alongside of, and in closely spaced relation to, the supporting means, a normally closed thermostatically operated electric switch in the casing closely adjacent the heating element and on the opposite side of the heating element from the supporting means and adapted to open and close at predetermined temperatures, electrical conductor means connecting the switch and heating element in series with each other, and including means accessible from the exterior of the casing adapted for 4connecting the conductor means to opposite sides, respectively, of a source 0f power.

2. A calibrator of the type described in claim 1 and characterized in that said supporting means is a tube of heat conducting material and at least at one end extends through an end wall of the casing and is open to permit insertion of the thermally responsive means.

3. A calibrator of the type described in claim 2 characterized in that thermal insulation is disposed in the ycasing in surrounding relation to the tube and heating element.

4. A calibrator for a thermally responsive control device of the expansible fluid type employing an elongated bulb of small diameter and comprising a hollow elongated casing of small cross section, an elongated metal tube of small diameter extending endwise of the casing and through the end walls thereof and being open at both ends, means securing the ends of the tube to said end walls, respectively, an elongated electrical heating element in the casing and disposed alongside the tube and substantially coextensive endwise therewith, a normally closed thermostatic electric switch in the casing exteriorly of the tube and in close heat exchange relation to the heating element, and electrical conductor means connecting the switch and heating element in series with each other, and including means accessible from the exterior of the casing adapted for connecting the conductors to opposite sides, respectively, of a source of power.

5. A calibrator according to claim 4 characterized in that clamp means are provided and conneet said switch and element to the tube so that they are supported by the tube.

6. A calibrator for a thermally responsive control device and comprising a hollow casing, supporting means in the casing adapted to receive a thermally responsive means of the device and to support it in the casing, said casing having a wall with an opening therein aligned with said support for permitting endwise insertion of the thermally responsive means into the casing in proper position on the supporting means, an electric heating element in the casing in closely spaced relation to the supporting means, a normally closed thermostatically operated electric switch in the casing between the supporting means and element and adapted to open and close at predetermined temperatures, electric conductor means connecting the switch and heating element in series with each other and including means accessible from the exterior of the casing adapted for connecting the conductors t0 opposite sides, respectively, of a source of power, a second normally closed thermostatically operated electric switch in the casing between the supporting means and element and adapted to open and close at a higher temperature than first mentioned switch, a by-pass circuit connecting the second switch in parallel with the iirst switch and in series with the element, and a normally open manually closable switch connected in the by-pass circuit in series With the second switch and accessible for operation from the exterior of the casing.

VINCENT J. EVANS.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,367,985 Weeks Jan. 23, 1945 2,383,756 Williams Aug. 28, 1945 2,456,030 Sohns Dec. 14, 1948 2,541,121 Sparklin Feb. 13, 1951 2,552,087 Cooper May 8, 1951 

